The Financial Times said the ISI gave access to the Chinese military to the modified Blackhawk helicopter and let a sample of its special "skin" be taken.

The helicopter, one of two used by a team of US Navy Seals, was said to have been modified to allow it to enter Pakistani airspace undetected by radar.

The Navy Seals tried to destroy the aircraft after it crash-landed, but part of the tail remained intact.

US officials have said there is reason to believe that Pakistan let the Chinese inspect the aircraft, but they cannot confirm whether it happened.

Relations between Washington and Islamabad were severely strained by the operation on 2 May, during which Bin Laden was killed at a compound in the Pakistani city of Abbottabad where he had apparently been living for several years.

Pakistan enjoys a close relationship with China, which is a major investor in telecommunications, ports and infrastructure.